Where is the Free Item field from a Purchase Order stored?

The field is on the ME23 screen but not in EKPO.

Table Name RM06E

Field Name UMSON

Data Element UMSON

Screen Field RM06E-UMSON

I've found references on OSS to EKPO-UMSON but this doesn't exist: we're on SAP_APPL 500 0009 SAPKH50009 for Logistics and Accounting.

Thanks,

Matt.